The main active principle in the solid composition of matter involved in the present invention is selected from chitosan, its derivatives or salts thereof. Chitosan is a well-known polysaccharide which is composed of β(1-4)-linked N-acetyl-D-glucosamine and D-glucosamine units. Chitosan is manufactured by alkaline treatment of chitin, a polymer forming the shell of inter alia insects and crustaceans. Commercially, chitosan is recovered from crab- and shrimpshells that are waste products from the fishing industry. When treating chitin with alkali, usually sodium hydroxide, N-deacetylation takes place, i e acetamido groups are converted to amino groups, as the chitin is transformed to chitosan. By controlling the alkaline treatment of chitin it is possible to manufacture chitosans with varying degrees of N-acetylation.
Physical properties of chitosan, its derivatives and salts thereof, which properties affect its utility, depend on the degree of N-acetylation, the {overscore (Mw)}, the molecular weight distribution and the distribution of N-acetyl groups. Furthermore, different acid addition salts and derivatives of chitosan exhibit different properties.
It is also known that chitosan, its derivatives and salts thereof are biologically active and inter alia show anti-microbial properties.
Chitosan and derivatives and salts thereof are used in many forms, such as in solutions for the control of microbial growth. Examples of such solutions are solutions used as teat-dipping agents to prevent onset of mastitis in lactating cattle, as in e g WO 98/48627, as well as solutions for other anti-microbial uses.
One problem encountered in the use of solutions of chitosan, or of derivatives or salts thereof, is lack of stability of such solutions, especially when stored at elevated temperatures.
The dissolution of chitosan, or of derivatives or salts thereof, or indeed of any polysaccharide, is often problematic when performed without vigorous stirring. Instead of dissolving, the polysaccharide material will form lumps with a gel-like shell efficiently prohibiting further dissolution of the material.
Furthermore, transportation of dilute solutions of chitosan, or of derivatives or salts thereof, is expensive and involves handling problems in preparation and use. Also, storage facilities for dilute solutions can be costly and therefore disadvantageous.
Another possibility to solve storage and transportation problems would be to prepare concentrated solutions. However, this is not possible since chitosan forms very viscous solutions already at a low concentration, preventing the preparation of highly concentrated solutions.
Another problem with chitosan solutions, and especially concentrated solutions, is that the viscosity decreases over time, due to hydrolytic degradation.